Currently, most televisions employ interlaced display technique for displaying images. The interlaced display can greatly reduce the bandwidth used for transmission of signals. However, when an image edited on a computer is to be displayed in an interlaced way on a television, quality of the image tends to be degraded due to a flicker feeling with respect to the image. This results from differences between display principles of the television and the computer, where the progressive display is used for the computer, and the interlaced display is used for the television. When converting the progressive display into the interlaced display, progressive pictures are divided into odd field pictures consisting of odd rows and even field pictures consisting of even rows, which are then displayed on the television at a field frequency of 60 Hz or 50 Hz, as illustrated in FIG. 1.
As can be seen from above, systems of televisions and computers are not compatible in display. However, markets of televisions and computers have already become confluent. Driven by the market force, an effective method capable of linking two systems is cried for.
One method used commonly is vertical filtering of brightness, which includes an N-order low-pass filter capable of storing N-row image data. The frequency spectrum of two adjacent rows with a relatively large bright-dark contrast is distributed in high frequency part of the frequency field. The use of the low-pass filter can suppress energy of high frequency components, thereby alleviating the bright-dark contrast of the adjacent rows, so that the flicker feeling caused by those adjacent rows will not occur in the image, and thus an anti-flickering function can be achieved.
FIG. 2 shows a method for implementing vertical filtering in the prior art. Pictures edited with a computer are stored in an external RAM. When data of the mth row and the nth column is to be displayed, firstly points of columns corresponding to three adjacent rows (the (m−1)th row, the my row, and the (m+1)th row,) are read into a in-chip register, and then are filtered through the low-pass filter, and thus new point y′(m, n) is generated to replace the corresponding point which has been filtered.
The method using the vertical low-pass filtering is disadvantageous in that an effect of a pixel transparency (an Alpha value) on anti-flickering has not been taken into account. There are different transparencies in different regions within an original picture, which greatly influences the visual effect. When adjacent rows are identical in brightness but quite different in transparency, the flickering effect may occur. If only vertical filtering of brightness is performed here, then the flickering due to a difference between the transparencies can not be avoided and hence such a flickering still fails to be avoided effectively.